From 40268dcd8dd57638a33ab44340ae130525e0a956 Mon Sep 17 00:00:00 2001
From: Felix Prasanna <91577249+fprasx@users.noreply.github.com>
Date: Fri, 25 Aug 2023 13:29:10 -0400
Subject: [PATCH] monitor: fix filecache calculations (#5112)

## Problem
An underflow bug in the filecache calculations.

## Summary of changes
Fixed the bug, cleaned up calculations in general.
---
 libs/vm_monitor/src/cgroup.rs    | 8 +++++---
 libs/vm_monitor/src/filecache.rs | 6 +++---
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/libs/vm_monitor/src/cgroup.rs b/libs/vm_monitor/src/cgroup.rs
index 84a1a07b9d..4f529d16fd 100644
--- a/libs/vm_monitor/src/cgroup.rs
+++ b/libs/vm_monitor/src/cgroup.rs
@@ -634,7 +634,7 @@ impl CgroupWatcher {
             .context("failed to get memory subsystem")?
             .set_mem(cgroups_rs::memory::SetMemory {
                 low: None,
-                high: Some(MaxValue::Value(bytes.min(i64::MAX as u64) as i64)),
+                high: Some(MaxValue::Value(u64::min(bytes, i64::MAX as u64) as i64)),
                 min: None,
                 max: None,
             })
@@ -654,8 +654,10 @@ impl CgroupWatcher {
             .set_mem(cgroups_rs::memory::SetMemory {
                 min: None,
                 low: None,
-                high: Some(MaxValue::Value(limits.high.min(i64::MAX as u64) as i64)),
-                max: Some(MaxValue::Value(limits.max.min(i64::MAX as u64) as i64)),
+                high: Some(MaxValue::Value(
+                    u64::min(limits.high, i64::MAX as u64) as i64
+                )),
+                max: Some(MaxValue::Value(u64::min(limits.max, i64::MAX as u64) as i64)),
             })
             .context("failed to set memory limits")
     }
diff --git a/libs/vm_monitor/src/filecache.rs b/libs/vm_monitor/src/filecache.rs
index 33c76de35e..8dd369c9f1 100644
--- a/libs/vm_monitor/src/filecache.rs
+++ b/libs/vm_monitor/src/filecache.rs
@@ -132,11 +132,11 @@ impl FileCacheConfig {
 
         // Conversions to ensure we don't overflow from floating-point ops
         let size_from_spread =
-            0_i64.max((available as f64 / (1.0 + self.spread_factor)) as i64) as u64;
+            i64::max(0, (available as f64 / (1.0 + self.spread_factor)) as i64) as u64;
 
         let size_from_normal = (total as f64 * self.resource_multiplier) as u64;
 
-        let byte_size = size_from_spread.min(size_from_normal);
+        let byte_size = u64::min(size_from_spread, size_from_normal);
 
         // The file cache operates in units of mebibytes, so the sizes we produce should
         // be rounded to a mebibyte. We round down to be conservative.
@@ -268,7 +268,7 @@ impl FileCacheState {
             .context("failed to extract max file cache size from query result")?;
 
         let max_mb = max_bytes / MiB;
-        let num_mb = (num_bytes / MiB).max(max_mb);
+        let num_mb = u64::min(num_bytes, max_bytes) / MiB;
 
         let capped = if num_bytes > max_bytes {
             " (capped by maximum size)"